Libraries and open source movement share some of the basic values and principles: openness, transparency and culture of sharing. Also, open source software offers some practical advantages particularly important for libraries, such as the focus on open standards. This has been recognized by individual libraries that use open source software and by IFLA Information Technology Section that has established the Open Source Working Group. Regardless, most public libraries still mainly use proprietary software. While some library-specific open source applications are widely used, such as various digital libraries software, others – such as library management systems – are not, mainly because of lack of technical support providers, perceived code immaturity and market saturation. However, when it comes to general purpose applications – word processors, graphics editors, database systems, spreadsheet applications and even desktop operating systems – there are no reasons not to use open source, considering that their quality and features are at equal or even higher level, in comparison with proprietary applications. Therefore, it is necessary to inform and educate library community on the benefits of open source software, in order to create prerequisites for its successful implementation and use in libraries.